by Jon F. Zeigler
Art by Glenn Grant, John Grigni and Ted Lindsey
For many years (most of my life, in fact) I've been working on ways to do better worldbuilding for science-fiction RPGs. Some Traveller players roll up characters, plan mercenary tactics, or design starships. I build solar systems.
Traveller was one of the first RPGs I ever played, and it's always been one of my favorites. Even so, one of the things that bothers me about it is the simplification that it applies to star mapping. The two-dimensional hex grid is easy to work with and fits the game's flavor well enough, but it's not very realistic. The real universe has depth.
One aspect of my study of astronomy has been the structure of the "solar neighborhood," the tiny corner of the galaxy surrounding Earth itself. This three-dimensional space strikes me as an ideal stage for adventure, a backdrop for humanity's first steps out into the universe. Unfortunately, the RPG industry doesn't seem to agree with me. The last RPG to use the solar neighborhood for a setting was 2300 AD, once published by GDW along with Traveller, but presently long out of print.
Still, let's see if it can be done. Let's think about how to design a campaign with Traveller flavor, presumably using GURPS rules, but set among the nearby stars of the real universe.
First, we need to consider all the implications of a three-dimensional geometry. The Third Imperium of GURPS Traveller owns 11,000 star systems, spread through an irregular two-dimensional region about 200 parsecs long and 140 parsecs wide. In three-dimensional space, assuming about one star system per 11.5 cubic parsecs, the same number of systems would fill a sphere about 62 parsecs across. In the Third Imperium, a ship with jump-6 capacity takes at least fifteen jumps to make it from Capital to Deneb or Terra. A similar 6-parsec-range ship in our three-dimensional Imperium would take only about five jumps to go from core to frontiers. A 3-D empire is more compact.
Related to this is the increased versatility of faster ships in 3-D space. In the Third Imperium, assuming about a 50% chance of a star system in any given hex, a jump-1 ship is likely to be able to reach three or four star systems, while a jump-6 ship can reach more than 60. That's a big difference, but it pales when compared to the 3-D situation. A ship with 1-parsec range in our 3-D universe is unlikely to find even one star within its range, but a ship with 6-parsec range can reach almost 80.
It appears that in order to get the same "feel" as in Traveller, we'll want to somehow limit the range of starships. One approach might be to make the jump ranges non-linear, so that the difference in range between a jump-2 and a jump-3 starship is actually less than that between a jump-1 and jump-2 starship. That has all kind of implications for the flavor of the game, though. Best not to try anything that radical.
Another option would be to cap the jump numbers. Suppose our campaign setting is only at early TL 10. Then (assuming the same technological progression as in standard GURPS Traveller) the most we can hope for is jump-2. That suggests an "open frontiers" campaign, set in the early days of starflight while humans first expand out from Earth.
Now, if we assume that jump-1 means a 1-parsec range, as in standard Traveller, we're likely to be disappointed in the results. Jump-1 starships in the Third Imperium are limited, but useful. Many worlds fall in the great "mains," chains of star systems that are all reachable by jump-1. Even a jump-1 ship can slowly leapfrog its way across most of the Imperium. In the 3-D universe, however, it's rare for two star systems to be within 1 parsec of each other, and there are no equivalents to the "mains." We will more than likely need to define a "jump-1" as covering some distance greater than one parsec. Exactly what that distance is should depend on the structure of nearby space. What distance is likely to give us the best potential plots? Perhaps we can find inspiration by looking at a map of nearby space. . .
The first survey of the solar neighborhood was compiled in the Gliese Catalog of Nearby Stars, the first edition being published in 1957. In the last few years, the European space probe HIPPARCOS was flown to compile an extensive catalog of stars, with distances measured to a higher degree of accuracy than was ever possible for Earth-based observatories. These catalogs are not entirely accurate or complete for even the close solar neighborhood, since very dim stars may be overlooked even when they are close by. Still, they should be sufficient for gaming purposes. Using the figures in the Gliese or Hipparcos catalogs, it's possible to apply the First In rules to do complete worldbuilding.
All of these data are available on the Web. By far, the best site to begin researching nearby stars belongs to Winchell Chung. He has a superb collection of resources for star mapping, world-building, science-fiction RPGs, and so on. His site is at http://www.clark.net/pub/nyrath/starmap.html. Another good resource is RECONS, a group of astronomers who study nearby stars. Their URL is http://cfa-www.harvard.edu/~thenry/RECONS.html. Finally, the best computer utility available for 3-D starmapping is probably the CHview program, designed by several fans of C. J. Cherryh's Alliance/Union stories. CHview comes with data files based on the Hipparcos data, and has a wide variety of options: the solar neighborhood can be viewed from any angle, "jump lines" of any specified length can be planned, and so on. It and its supporting data files can be downloaded from the Sol Station website: http://members.nova.org/~sol.
For this article, I used the CHview program and began investigating how nearby stars could be reached, assuming jump drives of varying range. I further assumed that the "jump drive" of our setting would only move starships between the gravity wells of stars, so that there would be no jumps to "deep space." Although such deep-space hops are possible in standard Traveller, the setting seems to imply that they don't happen often. In any case, if starships can only move from one star to another, that means that certain star systems will be "choke points" or "crossroads" of great strategic value. Such situations naturally give rise to conflict (and plot hooks).
As the range of our putative jump drive increases, stars begin to fall into chains and networks of accessible routes. When the range passes about 2 parsecs, several long chains of accessible stars appear, reaching out from Sol. In fact, the 2300 AD game assumed a normal "jump range" of about 7.7 light-years or 2.4 parsecs. This assumption is a trifle unsatisfactory, because there are a number of stars close to Sol that can't be reached by any combination of such short jumps. Also, when the jump range is this short, the accessible stars fall into narrow "arms" which connect only at Sol and tend to taper off into dead ends. If we increase the range to about 9 light-years, however, most of the previously-inaccessible stars link into the network. The network forms "trunks" and "webs" which connect to each other at several points, and extend indefinitely into deep space. This will help if we want the dynamic of the campaign to involve interactions between colony and colony, not just between colony and homeworld.
Setting the standard jump range to 9 light-years has another useful implication. If we assume that 9 light-years is a standard range for jump-2 ships, then a jump-1 ship can reach 4.5 light-years. This means that a jump-1 ship can safely travel from Sol to Alpha Centauri (4.4 light-years away) but could reach no other star system. That implies that Alpha Centauri would be colonized soon after the development of the jump drive, but the real burst of expansion would only occur some time later, after jump-2 engines were developed. Alpha Centauri would therefore be an interesting mix of frontier and civilized core, a place from which adventures could begin.
Now that we've decided how to implement our campaign's version of jump drive, we can start looking at nearby stars and deciding where to place important worlds. Let's take a quick tour of the 25 or so nearest star systems. We'll look at every star within 9 light-years (one jump-2 radius), and the most interesting ones out to about 12 light-years.
Nearest to Sol is Alpha Centauri, a famous trinary star system. The primary star is very similar to Sol, slightly larger and brighter. The largest companion is a smaller K0 V star. The system appears to be somewhat older than Sol, perhaps 6 billion years old. Most astronomers doubt that a double star like this one can have planets, but the First In rules allow for the possibility. In fact, the companion's orbit is fairly wide and has only moderate eccentricity, so even the minimum separation between the components is wide enough to allow both stars to have planets in the life zone. If Alpha Centauri hosts one (or even two) habitable worlds, then it's certain to be an early target for interstellar colonization.
The third component of the Alpha Centauri system is a tiny red dwarf star of spectral class M5 V. It's not clear whether this star is actually physically associated with Alpha Centauri, as the separation is extreme (over 10,000 AU). It is slightly closer to Sol than the bright pair, so by some reckoning it is the star closest to us. It is therefore often named "Proxima" Centauri. Aside from its small size, Proxima is unusual for the amount of its flare activity. It is one of the most active flare stars known.
The next-nearest star system is Barnard's Star, a lone M4 V red dwarf. Barnard's Star is believed to have at least one planet of about 500 Earth masses, somewhat larger than Jupiter. This star was once quite famous for the speed with which it shifts position in the sky, and was called "Barnard's Runaway Star." In fact, it is probably a very old member of the galactic halo, currently cutting across the galactic disk against the motion of most other stars in our neighborhood.
As we might expect, most stars in our neighborhood are ordinary, even rather dull, red dwarfs. The next two systems on our list are perfect examples: Wolf 359 and Lalande 21185. Oddly, these two stars are not only close to Sol, they are also quite close to each other, so they form a matched pair of "stepping stones" leading outward from Sol toward galactic north. Lalande 21185 is believed to have an unseen companion of about 0.01 solar masses, a super-Jovian planet or "brown dwarf" star. Wolf 359 is one of the least luminous stars known, only about 1/63,000 as bright as Sol. Both stars are significantly older than Sol.
The next star on the list is also the brightest star in Earth's sky: Sirius. The primary, Sirius A, is a brilliant A1 V star about 23 times as luminous as Sol. Sirius is clearly a young star, since A-class stars don't last very long. It appears to belong to a group called the "Sirius supercluster," a clan of stars all of which are only a few hundred million years old. Members of the Sirius group are scattered all over our sky, because Sol is currently moving through the middle of the cluster. Sirius might be a good place for industrial outposts to be set up, using torrents of free energy from the primary and mining metal-rich planetoids.
Sirius has a companion, Sirius B, which was one of the first "white dwarf" stars ever discovered. Although the companion has almost the same mass as Sol, it is only a few thousand miles across and has very low luminosity. A few astronomers have speculated that Sirius B was still a red giant star quite recently (within the last few thousand years). Although this would contradict much of what we think we know about the evolution of dying stars, we do know that Sirius B is unusually bright and hot for a white dwarf, and therefore recently formed. Meanwhile, many ancient sources (Babylonian, Greek and Roman) all refer to Sirius as reddish in color. . .
Next on the list is a double-star system tagged UV Ceti. The two components of this system are matched red dwarf stars, both with less than 5% of the Sun's mass. No visible stars are known to have lower mass than the UV Ceti components. The small component is a wildly-variable flare star, erupting every few hours. The UV Ceti system is probably of an age comparable to Sol. While it is very unlikely to host a habitable planet, it is interesting as a "stepping stone" system. Not only is it the last star system within a 9-light-year radius from Sol, it is also one of the best jumping-off points for travel from Sol to systems such as Tau Ceti, Epsilon Eridani or Epsilon Indi.
From this point on, we won't discuss individual red-dwarf stars. Suffice it to say that there are many of them. Out of the 25 star systems closest to Sol, 19 are composed of one or more red dwarf stars. Given our assumptions regarding the jump drive, these systems are most likely to be interesting as stepping stones, places where outposts or fuel depots will be constructed. Under the First In rules, any one red dwarf isn't likely to host an Earthlike world. Still, the sheer number of such stars means that many habitable planets are likely to circle them. Feel free to design the occasional red-dwarf system with a freakishly Earthlike world.
Aside from red dwarfs, the next interesting star is Epsilon Eridani, at about 10.5 light-years from Sol. This is a single K2 V star, somewhat smaller and cooler than our sun. For years, it was considered a good candidate for an Earthlike planet. However, recent observations make it clear that Epsilon Eridani is quite young, probably about 500 million years old. It may very well have planets which are still in the process of formation, but none of them will be likely hosts for life. This system might be a reasonable place for a scientific outpost, studying the process of planetary birth. It is also likely to be metal-rich, so industrial outposts might be set up there as well.
The 61 Cygni system is next, at about 11.1 light-years. Strangely, although 61 Cygni is fairly close to Sol there is no direct route there using our assumption of jumps up to 9 light-years. There simply aren't any other stars directly between Sol and 61 Cygni, so the quickest path is indirect and takes four jumps. 61 Cygni is a double system, with stars of class K5 V and K7 V. The pair's separation is fairly wide, so both stars may have complete systems of planets. In fact, it's believed that one or the other (probably the A-component) has a gas giant planet of about 2,500 Earth-masses. 61 Cygni is a possible location for an Earthlike planet, although each star is fairly small and dim so any planet in its life zone is likely to be tide-locked. The system is not likely to be much younger or older than Sol.
Epsilon Indi is a single star of class K5 V, similar to either of the components of the 61 Cygni system. It isn't known to have any planets, although there is no reason to suspect otherwise. Again, it's possible for this star to have an Earthlike world, although any such world would probably be so close to the star as to be tide-locked. Epsilon Indi is probably about the same age as Sol.
The last star in our tour is Tau Ceti, probably the most likely candidate (after Alpha Centauri) for human colonization. At about 11.8 light-years, it's only two jumps from Sol. It's not known to have planets, but it is more than luminous enough to have Earthlike worlds that are not tide-locked. Its spectrum reveals a somewhat unusual composition, slightly poorer than Sol in some metals, but much richer in others. If any of its planets are life-bearing, this might lead to odd local biochemistries (and might also make the planets resource-rich).
If we build a map of these stars, using pencil and paper or a utility like CHview, we'll find that the stars nearest Sol form three large clusters. The largest of these is reachable through Barnard's Star, UV Ceti or Sirius. It includes Epsilon Eridani, Epsilon Indi and Tau Ceti. Further out, this cluster links through a swarm of red-dwarf systems to many more Sol-like stars in several directions from Sol. This is likely to be the primary direction for interstellar expansion, if humans ever learn how to travel between stars at all. Any major Earth-based cultures of the early interstellar era will probably rush to stake claims to strategic systems or Earthlike worlds in this direction.
In almost the opposite direction, through Wolf 359 or Lalande 21185, is another large cluster. Aside from Procyon, most of the nearby members of this cluster are dim red dwarf stars. There are Sol-like stars in this direction too, but they are more distant and can only be reached through a "star-desert" of red dwarfs. Humans who settle in this direction are likely to be those who can think in the long term, developing a chain of outposts to reach the more distant prize worlds. This direction may attract second-rank powers or isolationist groups who wish to avoid the "land rush" into the first cluster.
The third cluster is smaller and more isolated, and can only be reached by skirting the edges of the first. Eventually, however, we reach 61 Cygni. Beyond that are several Sol-like stars, any of which might have a new Earth in orbit. Again, this cluster is likely to attract pioneers, risk-takers and isolationists.
There we have it. Our campaign setting is placed sometime in the next few centuries, after human beings have settled a few dozen star systems but before they've expanded so far as to lose contact with Earth. We have a civilized Core, and three frontier "sectors" which might each develop a distinctive flavor. There might be three or four Earthlike worlds, a dozen marginal planets, and any number of barren rocks with outposts in place. Now to fill in the details -- but that's your job. Have fun!
Article publication date: June 25, 1999
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